In the field of ballistics, the term precision describes the ability of a projectile, fired from a weapon system, to follow a predicted trajectory and hence hit an expected target; a precise projectile will, by definition, follow a predicted trajectory more closely than an imprecise projectile. Ballistic precision is commonly measured using the circular error probability (CEP).
In most cases, it is desirable to have a precise projectile. However, the unit cost of a projectile tends to rise with increased precision. Accordingly, it is generally understood that in designing projectiles, the benefit of providing a particularly precise projectile must be balanced against the costs of such provision.
It is known to have a kit, such as the XM1156 Precision Guidance Kit (as may be supplied by Alliant Techsystems to the US Army), whereby a standard (i.e. non-guided) 155 mm artillery shell may be converted into a guided munition. The kit comprises means for controlling the trajectory of the projectile. Such controlling means may include a set of control surfaces, a processor, and an actuator for moving the control surfaces in response to a correcting signal from the processor. The processor may be interfaced with Global Positioning System (GPS) and Inertial Navigation (IN) sensors to determine the correcting signal which is to be applied.
The kit, which further includes a fuze, can be retrofitted into a shell by detaching the fuze section of the shell from the body section of the shell and then attaching the kit to the body section. The kit may therefore give users the option of converting munitions and thus selecting the precision of each round fired.
However, the Precision Guidance Kit (PGK) may have a deep intrusion body that necessitates the removal of some of the shell's explosive payload in order to fit the PGK instead of the original fuze.
Further, the act of replacing the original fuze with the kit may be undesirably time consuming, particularly given the urgency with which a muniton may need to be fired. Indeed, it may not even be possible to replace the original fuse with the kit on the battlefield, for example if some of the payload must be removed as described above.
Further, the kit may only be applicable to munitions which have a detachable fuze. Where the munition does not originally have a fuze, the kit cannot readily be applied.